Security cards are widely used for various applications such as identification purposes (ID cards) or financial transfers (credit cards). Such cards typically consist of a laminated structure consisting of various plastic lamellae and layers wherein one or more of them carry information, e.g. alphanumeric information, logos, a picture of the card holder, etc. A principal objective of security cards is that it cannot be easily modified or reproduced in such a way that the modification or reproduction is difficult to distinguish from the original.
Writable cards wherein the user can store digital information are also known, e.g. cards comprising a magnetic strip, optically recordable cards or cards comprising an electronic chip, sometimes called ‘smart cards’.
In a number of application fields, the average daily usage of cards has augmented substantially from less than 1 time per week to 4 times per day. The card body has to withstand not only this increased usage, but also the associated storage conditions. Cards are no longer safely tucked away in cabinets at home or seldom-opened wallets, but are now loosely put away in pockets, purses, sport bags etc.—ready for immediate use.
In combination with higher stress levels seen by the card body, the issuers at the same time want to extent the validity periods of their cards, because of the high cost of the embedded electronics. Marketeers want to keep their cards looking shiny and brand-new in the hands of their customers. And smart issuers will demand from their suppliers to assume all costs related to premature return from the field.
The combination of these factors—higher card demand, more frequent usage, less careful storage, longer validity requirements and higher total costs, forces card makers and issuing bodies to look for higher performance materials for the card body.
PVC (polyvinylchloride) is the most widely used material for plastic cards, because of its ease of printing and laminating and its low cost. The biggest disadvantage is the low durability of the card body, resulting in an effective lifetime of only 1-3 years, much lower than the lifetime of the often expensive chips. Other materials like Teslin and ABS are only suitable for very low-end or single-use cards. PC (polycarbonate) can be used for longer-life and more secure ID cards, but has a high production cost and a low resistance to torsion, scratching and chemicals.
PET-G (polyethylene terephthalate glycolised) is a kind of amorphous polyester which has not been toughened like crystalline polyester but rather processed to become more compatible with standard PVC card manufacturing. Durability of PET-G cards is comparable to that of PVC cards.
PET-C (crystalline polyethylene terephthalate) is a material that is very durable and resistant to mechanical influences (flexion, torsion, scratches), chemical substances, moisture and temperature ranges. Untreated PET-C cannot be sealed or laminated to itself or to other materials, but require additional coatings or layers to accomplish this.
Lamination of PET-C films for preparing credit cards is known from U.S. Pat. No. 5,171,625 (ICI) which however discloses only an all polyester composite film structure for a credit card. An opaque, biaxially oriented polyester support core film and a clear, biaxially oriented polyester top film are heat sealed together by means of isophthalate-terephthalate copolyester based dye receptive or printable receiver film(s) which are sandwiched between the top surface of the core film and one surface of the top film. There is no disclosure of lamination to other type of materials such as PVC or PC. The co-extruded dye receptive or printable receiver films also have a large thickness of 0.5 μm up to 50 μm.
WO 2009/063058 (AGFA GEVAERT) discloses the lamination of a security laminate comprising a biaxially oriented polyester lamella and an adhesion system associated therewith on other type of materials such as PVC and PC. The adhesion system includes a layer system comprising a polyester, a polyester-urethane or a copolymer of a chlorinated ethylene, the layer system being contiguous with the polyester lamella during at least part of the biaxial orientation and having a thickness of at least 1.0 μm. In the examples, the layer system is mostly based on copolymers of chlorinated ethylene exhibiting improved peel strength with increasing thickness of the layer system. The best adhesion results are obtained for layer system thicknesses of 2.7 μm to 25.5 μm. Such a large thickness however reduces the production speed of security laminates and thus productivity. In addition, bank cards, credit cards, driving licenses and the like are required to have a format as specified by ISO 7813, i.e. having the dimensions 85.60 mm×53.98 mm and a thickness of 760 μm±80 μm. A large thickness of the adhesion system reduces the options for incorporating laminates and layers within the thickness of 760 μm of ISO 7813.
Since methods for falsification and counterfeiting of security documents continue to develop and improve, it remains a constant battle to protect security documents against falsification and counterfeiting. Therefore a need exists to provide simple and cost-effective methods for securing documents which also have a longer life time despite more frequent usage and less careful storage.